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Mineral fuel is a substance typically obtained from the earth that burns in presence of air to produce energy with or without releasing gasses in large quantities. Mineral fuels, like coal and petroleum, are a unique kind of economic deposit. These mineral fuels are the main source of energy production and are commonly classified as non-renewable forms of energy.
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Key Terms: Mineral fuel, CNG, Hydrocarbon, Carbonification, Fossil fuels
What are Mineral Fuels?
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Mineral fuels are classified as natural or primary fuels and derived or secondary fuels. When the fuel is present in its natural state, it is usually referred to as natural fuel. When the fuel is processed to improve its quality, it is known as derived fuel. Mineral fuels are quantified by calorific values which are the amount of heat liberated by the complete combustion of a unit mass or volume of fuel. For liquid or gaseous fuels, the volume of fuel is measured while for solid fuels mass of fuel is measured to find out the calorific values.
Characteristics of an Ideal Mineral Fuel
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- High calorific value.
- Cause no or fewer pollution gasses on combustion.
- Low cost and easily available.
- Easy to handle, store and transport.
- Moderate ignition temperature.
- Moderate rate of combustion.
Coal
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Coal is a complex combination of carbon, hydrogen and oxygen compounds. It is found in either coal mines deep under the surface of the earth or open cast mines.
Formation of coal
It is thought that millions of years ago, the ground below the forests was split open by natural forces such as earthquakes and volcanoes. The forests got buried under layers and layers of sediments. It is also believed that trees may have died naturally and got buried under layers of sands or soils for millions of years. Thus, the trees had no contact with oxygen. Consecutive layers of sediments sealed the buried plants. Over millions of years, these deposits were subjected to tremendous pressure and heat leading them to transform into coal. The chemical process involved in the transformation of plant matter into coal is known as carbonisation.
Formation of Coal
The carbon content of coal varies with the variety of the coal. With the high temperature and pressure of the Earth and the longer time of the coal being hurried under the Earth, the carbon content in it increases. The types of coal are as follows:
- Peat: It is the variety of coal that formed more recently than the others. It is light brown. It has minimum carbon content and produces less heat and more smoke on burning.
- Lignite: It is also known as soft coal. It is brown too but has more carbon than peat.
- Bituminous coal: It is (was) used in common household coal. It is the most abundant coal in India. It is compact, black, contains more carbon and produces more heat than peat and lignite.
- Anthracite coal: It is the hardest coal having maximum carbon. It is difficult to ignite, so it is not used for household purposes, it is mainly used for industrial purposes.
Carbon Content and Moisture of Coal
The types of coal derivatives attained by the destructive distillation of coal are as follows:
- Coke: It has 98 % carbon content. Its main features are porous, tough, and black. It is mostly used in the extraction of metals from their ores. It also finds its usefulness in making fuel gasses like water gas and producer gas.
- Coal tar: Coal tar is a blend of different carbon compounds. It is a thick, black liquid that usually comes with an unpleasant odor. Coal tar, typically upon fractional distillation, gives several chemical substances which are used in the preparation of dyes, explosives, paints, and more.
- Coal Gas: Coal gas contains hydrogen, methane and carbon monoxide. It is an excellent fuel. It has a high calorific value.
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Petroleum
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It is a fossil fuel that is dark brownish to green in color and viscous liquid. It gives a strong foul smell due to sulphur containing compounds in it. It is commonly called crude oil. The economies of countries depend to a great extent on petroleum wealth, which justifies it's being called black gold.
Origin of Petroleum
Petroleum is a complex mixture of solid, liquid and gaseous hydrocarbons, associated with saltwater and earthy particles. It is generally found trapped between two impervious rocks. It is thought that petroleum is formed by the anaerobic decomposition when extremely small sea animals and plants got buried in the sea bed millions of years ago.
Occurrence of Petroleum
Petroleum is found at a moderate depth (500 m to 200 m) between the two layers of impervious rocks. Since petroleum is lighter than water, it floats over it. Natural gas is usually found above petroleum, trapped between the rock cap and petroleum layer.
Refining of Petroleum
Before being put to use, petroleum is purified or refined. The method of separating the various components of petroleum from one another is known as petroleum refining. This is done by a process of fractional distillation. The process is based on the principle that the different components of petroleum have different boiling points.
Uses of Petroleum
- Petroleum products are used as fuels.
- Make lubricating oils, and Vaseline to use as lubricants.
- Paraffin wax and other by-products of petroleum are used to make candles, polishes, waxed paper, waterproofing, etc.
- Production of medicines, ointments, face creams and cosmetics.
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Natural gas
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Natural gas is believed to have formed millions of years ago along with petroleum when microscopic sea plants & animals died & got buried under the sand & mud. These plants & animals under anaerobic conditions transformed into gas.
Composition of Natural Gas
It comprises mainly methane (about 85%), ethane (about 10%) propane (about 3%) and butane. Natural gas when compressed at high pressure is called CNG (compressed natural gas). CNG is used for power generation.
It is widely used as a fuel for transport vehicles because it is less polluting. It can be delivered to homes and factories via pipes.
Occurrence
It is usually found trapped between impervious rocks, and occasionally along with petroleum & sometimes without petroleum.
Uses of natural gas
- It can be used as fuel because it has a high calorific value.
- Also, as a source of hydrogen & carbon
Things to Remember
- Bitumen, which is a petroleum product, is used in place of coal tar for metalling the roads.
- Mineral Fuels are fuels formed from dead, decaying plants and animals buried deep under the earth.
- Inexhaustible natural resources are sources that are present in unlimited quantities in nature and are not likely to be exhausted by human activities. Examples: Sunlight, air, etc.
- Exhaustible natural resources which are in a limited amount can be exhausted by human activities. Examples: Forests, coal, petroleum. minerals, wildlife, natural gas, etc.
- Natural gas is stored as CNG under high pressure. CNG is used for power generation. It is also used as fuel for transport vehicles because it is less polluting. It is a cleaner fuel.
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Sample Questions
Ques. Describe characteristics of coke. List one key use of coke. [3 marks]
Ans. Characteristics of coke:
- Coke is tough.
- It is porous and black in color.
- It is one of the purest forms of carbon.
One of the key uses of coke is that it is used in the production of steel and the extraction of many metals.
Ques. Explain the process of formation of petroleum. [3 marks]
Ans. Petroleum is produced from the dead bodies of organisms living in the sea. When these organisms die, their bodies settle down at the bottom of the sea. These bodies get compressed under layers of sand and clay. Over millions of years, in the absence of air, and under high temperature and pressure the dead bodies are transformed into petroleum and natural gas.
Ques. Describe how coal is formed from dead vegetation. What is this process called? [3 marks]
Ans. About 300 million years ago the earth was covered with dense forest in low lying wetland areas. Because of numerous natural processes, like flooding and earthquakes, these forests got buried under layers of soil. When the soil was deposited layer by layer over them, they were compressed. Under high temperature and pressure, the plants got transformed into coal slowly. This process is called carbonisation.
Ques. List the several advantages of using CNG and LPG as fuels? [4 marks]
Ans. Advantages of CNG and LPG:
- CNG and LPG are clean fuels.
- Both of their costs are low.
- Both CNG and LPG can be used directly for burning
- They are easily available.
- They minimize the rate of pollution.
Ques. Why is coal called buried sunshine? [1 mark]
Ans. Coal is known as buried sunshine because it is found buried under the earth, and is as important a source of energy just like sunshine.
Ques. Name and describe briefly the methods followed during extraction. [4 marks]
Ans. Mining, drilling and quarrying are various methods of extraction. Mining is a method of extraction of minerals from rocks under the earth’s surface.
- Opencast mining: Here, minerals lying at shallow depths are extracted by removing the surface layer.
- Shaft mining: In this, deep bores are made to reach mineral deposits lying at large depths.
- Drilling: Deep wells are bored into the earth to take out minerals.
- Quarrying: It is the method in which minerals lying close to the surface are extracted by digging them out.
Ques. What are Liquid Fuels? [3 marks]
Ans. Liquid fuels like furnace oil are mainly used in many industrial processes. Most of the liquid fuels in use nowadays are made from the fossilized remains of animals and plants formed under pressure and heat in the Earth's crust. However, there are many types of liquid fuel such as ethanol, hydrogen fuel (for automotive uses), biodiesel, and jet fuel.
Ques. Explain if Gasoline is a Mineral? [2 marks]
Answer: No, it isn’t. Gasoline is a chemical formulation, which does not occur in nature. It is made after refining crude oil and can contain other chemicals and compounds, which are mixed during the process. Minerals naturally occur in nature and are defined generally as inorganic, though they might contain a few elements associated with organic compounds like carbon.
Ques. Why should we conserve fossil fuels? [3 marks]
Ans. Because the known reserves of fossil fuel are limited. Another issue with fossil fuels is that they are causing air pollution, and their use is linked to global warming. So, we must use fuels only when it is necessary. By this, we can save these fuels for the Manufacture of many substances which are made from these.
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